What was the 340 6 pack rated at.
I see nothing in the op's build that would add another 50 hp over the factory 275, maybe 15 -20 extra.
The Rpm intake is probably good for another 5 hp over the 340 unit given the combo. camshaft maybe 10 headers maybe 10.
Don't compare a low comp 340 to a 68 340. two different animals.